In its simplest form, a seal assembly for a rotary bearing or the like, such as used for sealing the wheel spindle assembly of a vehicle, includes at least one annular flexible seal member attached to a seal casing. The seal most often takes the form of one or more flexible members each having a lip urged against an opposed casing or other member to form a sealing interface around the circular line/face of contact. This sealing action allows relative rotation between the coaxial, rotating component parts, while maintaining good seal efficiency to prevent entry of foreign material into the wheel spindle bearing, such as salt, road grime and other debris. The seals of prior art seal assemblies are primarily formed of a molded elastomer material such as rubber, but can also be made of less flexible, but lower friction plastic materials, such as polytetrafluoroethelene (PTFE).
Especially in the area of wheel spindle technology, a seal assembly can experience rapid radial and/or axial vibrations between the inner and outer casings. These vibrations can cause instability of the sealing lips and excessive deterioration of the seals, especially along the circular lines/faces of contact with the opposing casing. As the lips of the seals deteriorate, they lose their ability to flex rapidly enough to maintain the critical continuous sealing contact with the opposing casing, and the seal integrity is further eroded. In addition salt, road debris, or other corrosive materials that are commonly encountered in every day use of a vehicle, can accelerate this deterioration and resultant loss of flexibility, thereby further exacerbating the problem. Eventually, contamination of the lubricant within the seal assembly leads to rough bearing operation, along with increased noise and heat, and thus a shortened seal/bearing life.
An example of a type of rotary seal assembly with one or more flexing seal lips providing circular face contact(s), that has had success in use, but tends to be subject to the above disadvantage, includes the seal assembly shown and described in Christiansen U.S. Pat. No. 4,497,495, owned by the assignee of the present invention. As disclosed in this patent, a seal member is attached to an inner casing and has two free lips that flex in response to their own resilient memory against the inside sealing surface of an outer casing to form two seal interfaces. By free flexing contact with an annular casing, the lips facilitate good sealing contact around two circular faces of contact. But as the seal member becomes unstable and deteriorates due to the aforementioned causes, its ability to maintain this flexing contact is impaired, resulting in a reduction in the effectiveness of the seal interfaces.
Another approach that has been proposed for sealing similar rotatable parts relies on the use of a spring to bias a relatively thick, O-ring type seal into sealing contact with an adjacent co-axial, sealing member. Two examples of this type of seal assembly are shown in Pat. No. 2,760,794 issued to Hartranft and U.S. Pat. No. 4,841,183 to Dohogne et al. The '794 patent also teaches the need for the spring to bear against a washer, which in turn, bears against the O-ring. In this manner, the O-ring is indirectly biased into sealing engagement within the adjacent sealing surface. Also, both patents teach face-to-face sealing contact of the seal rather than flexing of a relatively thin sealing lip that provides the more efficient sealing interface along a circular line of contact. Unfortunately, while this type of prior art seal assembly has increased sealing interface stability and works well in relatively shielded environments, it leaves much to be desired in a hostile environment, such as encountered in protecting the bearing assembly of a vehicle wheel spindle assembly.
Thus, the need is identified to provide an improved seal assembly that is not only characterized by improved seal effectiveness and integrity, but also by a longer useful life, especially in relatively hostile environments. Indeed, the present invention discloses a novel solution to the identified problem that is prevalent in such environments as experienced by wheel bearing assemblies for vehicles.